Micro surface mount devices (microSMDs), also known generically as “flip chips”, are wafer level scale packages. Individual micro-SMD chips are first fabricated on a semiconductor wafer using standard semiconductor processing techniques. Typically, horizontal and vertical scribe lines of aluminum or some other type of conductive metal separate each microSMD chip on the wafer. Once the integrated circuitry and metallization interconnect is fabricated on the wafer, solder balls are formed on each of the chips on the wafer. The solder balls are used to later electrically and mechanically attach the microSMD chips to a substrate, such as a printed circuit board, after the chips are singulated from the wafer.
A fabricated wafer undergoes a number of steps to prepare the microSMD chips for mounting onto a printed circuit board. Initially the back surface of the wafer is ground to reduce its thickness and then coated with an epoxy material. The epoxy prevents chipping of the wafer during dicing. It also provides a surface for marking the chips with part numbers, company logos, and the like. Next the wafer is probed and each micro SMD chip is individually tested to identify operational and non-operational devices. A dicing machine then saws the wafer, along the scribe lines, to singulate the individual chips from the wafer. For more information on micro SMD packaging, see “MicroSMD—A Wafer Level Chip Scale Package”, by N. Kelkar, Mathew H. Takiar and L. Nguyen, IEEE Transactions on Advanced Packaging, Special Issue on Wafer Level Packaging, pp. 227-232, Vol. 23, No. 2, May 2000.
FIG. 1 is an illustration of a current microSMD package 100, including an integrated circuit die 120 with as solder balls 130 shown on the active side of the die. An epoxy coating 110 has been applied to the inactive side of the die. This type of package has a number of disadvantages. One problem with the aforementioned microSMD package is that epoxy material coating 110 on the back surface of the micro SMD semiconductor is a relatively poor thermal conductor. As a result, the only viable heat transfer path from the package is via solder balls 130 on the front or active side of the package. This tends to limit the uses for microSMD chips to relatively slow, low density and low powered applications. Since high-powered, high-speed integrated circuits usually run “hot”, microSMD chip packages have generally been a less than ideal for such applications. The use of a heat sink on a microSMD chip has been contemplated. However, attaching a heat sink to a microSMD after singulation is a difficult, tedious task that is expensive and difficult to automate.
Accordingly, an apparatus and method for a wafer level chip scale package heat sink is therefore needed.